The Storm Prediction Center in Norman, Oklahoma, had warned that a "substantial tornado risk" could develop in portions of the Southern Plains and Ozarks late Monday.

A series of violent thunderstorms dropped tornadoes near Oklahoma City and in the rolling hills south of the capital.

"You are in a life-threatening situation," forecasters declared when they declared a tornado emergency for Roff, population 725, and Hickory, population 71. "Flying debris will be deadly to those caught without shelter."

Television images showed at least three homes destroyed, multiple overturned vehicles and trees torn limb to limb. A roof lay near a hay barn after the first tornado reports from near Wynnewood along Interstate 35.

The Oklahoma Highway Patrol closed five miles of the main roadway between Oklahoma City and Dallas as the storm approached. It opened about 15 minutes later.

Meteorologists said twisters with wind speeds above 111 mph were possible from eastern Oklahoma to central Arkansas. Hail 2 inches or more in diameter is possible from eastern Texas to southeastern Kansas.

About 41 million people from Houston to Sioux City, Iowa, are at risk for some type of stormy weather.

While the threat was less farther north, forecasters issued a tornado warning for a storm near Lincoln, Nebraska.